.form-div{
    width: 40%;
    margin: 0 auto;
}

.form-control{
    text-align: center;
}

.btn.btn-primary{
    margin: 10px 0 0 10px;
    float: right;
}

.tips{
    color: red;
    font-size: 12px;
    margin-bottom: 10px;
}

.wrong{
    border-color: red;
    color: red;
}